Technical Field
The present invention relates to photovoltaic cells, and more particularly to devices and methods for improving absorber structures by preventing mass migration between grains in the structures.
Description of the Related Art
Photovoltaic devices often include exotic materials that are both rare and often toxic. For example, thin-film materials of the type Cu(In,Ga)(S,Se)2 (CIGS), while efficient, include rare indium metal, which is expected to be of high cost and short supply in future large-scale photovoltaic device production—an issue which is further exacerbated by the growing indium consumption for thin film display production. Other materials such as Cu2S and CdTe have also been proposed as absorbers but while Cu2S suffers from low stability in devices, rare tellurium and toxic cadmium limits CdTe usage.
Polycrystalline Cu2ZnSnS4 (CZTS) is an emerging material for solar cell absorbers which is cheap and earth-abundant. Large grain structures are good for device performance; however, grooves formed between large grains often become a shunting path (through which a buffer layer, such as CdS, makes contact to a bottom electrode). Sometimes a CZTS film delaminates off a substrate (typically Mo coated glass) during deionized (DI) water rinsing. It appears that capillary force exerted by DI water into the grooves is one of the causes of the film failure.